The mechanical pump comprises a pump rotor with radially slidable vanes rotating in a radially shiftable control ring, whereby the control ring is pushed by a first control chamber into high pumping volume direction. The pump comprises a pressure control system for controlling the discharge pressure of the pressurized lubricant at the pump outlet port. The pump is provided with a first pressure conduit which connects the pump outlet port with the first control chamber. The pump is also provided with a pressure control valve which controls the pressure in the first pressure control chamber.
A variable displacement lubricant pump is described in WO 2005/026553 A1. The pressure control valve keeps the pressure of the pressurized lubricant provided by the pump at a more or less constant level independent of the rotational speed of the pump rotor. This is realized by opening and closing a pressure control port of the control valve, whereby the pressure control chamber of the pump is connected or disconnected to the atmospheric pressure in the lubricant tank. The lubricant pressure demand of the engine is not constant, however, but depends on some working conditions of the engine, for example, on the lubricant temperature and on the rotational speed of the engine.